The present invention relates to a control system for an internal combustion engine, and more specifically to a control system for controlling a swirl control valve of an intake system for an internal combustion engine of a type having a stratified charge combustion mode and a homogeneous charge combustion mode.
Recently, the technique of in-cylinder direct fuel injection in a spark ignition engine such as gasoline engine is under development to significantly improve the fuel efficiency and emission performance by using stratified charge combustion and homogeneous charge combustion.
In a low and medium load region, a control system for such a type operates an engine in a stratified combustion mode by injecting fuel directly into a combustion chamber during the compression stroke so as to produce a stratified combustible mixture only around the spark plug. The thus-achieved stratified combustion enables stable combustion with an ultra lean mixture, and hence significant improvement in the fuel efficiency and emission performance of the engine.
In a high load region over a predetermined engine load, the engine is operated in a homogeneous combustion mode to meet a demand for higher output torque. In the homogeneous combustion mode, fuel is injected during the intake stroke so as to produce a homogeneous air fuel mixture. (In some examples, a fuel injection valve is provided separately in an intake port.)
The control system changes over the combustion control mode between the stratified combustion mode and the homogeneous combustion in accordance with one or more engine operating conditions.
An in-cylinder air flow condition is important to create a stratified mixture efficiently in a combustion chamber in the stratified combustion mode. A swirl control valve is a device disposed in or near an intake port, for regulating an intake air flow to control the in-cylinder air flow condition. In the stratified combustion mode, the swirl control valve throttles the intake air flow by decreasing its opening and thereby help create a strong swirl to achieve the stratified combustion. In the homogeneous combustion mode in which such a strong swirl is not needed, the opening of the swirl control valve is switched to an opening degree adapted to the homogeneous combustion mode.
Japanese Patent Provisional (Kokai) Publication No. 7(1995)-293260 shows a swirl control system for changing over the opening of a swirl control valve between an opening degree desired for the stratified combustion mode and a degree for the homogeneous combustion mode. This swirl control system closes the swirl control valve to produce the swirl flow in the stratified combustion mode, and in the homogeneous combustion mode in a high load operating region excepting a region near full throttle. The swirl control valve is fully open in the homogeneous combustion mode in the high load operating region near the full throttle.